Turbochargers are well known and widely used in combustion engines. Herein exhaust gas coming from the engine is supplied to a turbine wheel which drives a compressor wheel for compressing air which is charged to the combustion chambers of respective cylinders. The thus compressed air supplies the combustion chamber with more oxygen to enhance the combustion and thus to generate more power. However, as exhaust gas having a smaller pressure is supplied to the turbine wheel when the rotation speed of the engine is low, the air supplied to the combustion chamber is compressed less, which results in a so-called “turbo-lag” for low speed ranges. A known solution for overcoming this turbo-lag is to provide an electric motor for the turbocharger which additionally rotates the compressor wheel when the rotational speed of the engine is low for securing the pressure of the air supplied to the combustion chamber.
According to document U.S. Pat. No. 6,449,950 B1, there is provided a turbo charger having an electric motor for assisting the rotation of a rotor employing a shaft carrying a turbine wheel accommodated in a turbine housing and a compressor wheel accommodated in a compressor housing. The shaft is supported by a bearing accommodated in a center housing and the electric motor is accommodated by both the compressor housing and a motor housing casting. The center housing is located between the motor housing casting and the turbine housing.